1. Field of the Invention
The present invention relates to a contact tip for arc welding.
2. Description of the Prior Art
Copper is usually used as the material for contact tips for arc welding, because copper is relatively cheap and easy to machine. However, a contact tip constructed of copper has insufficient durability because it can be seriously abraded and sometimes becomes fused to a welding wire when it is excessively heated by a large amount of resistance heat due to a large welding current acting on a small contact area.
To improve thermal durability of the contact tip, Japanese Utility Model Publication SHO 62-77671 proposes to construct the contact tip from hard conductive ceramics, and Japanese Utility Model Publication SHO 51-21081 also proposes to form an anti-oxidation alloy layer through diffusion at the feed surface where the welding wire slidingly contacts the tip.
However, in the case of a conductive ceramics material, there is a problem that cracks tend to initiate at high temperatures because ceramics are brittle. Also, in the case of an alloy layer, there is a problem that the alloy layer tends to flake from the base metal due to a difference in thermal expansion coefficients. As a result, no great improvement in durability can be obtained in the prior art countermeasures.